1. Technical Field
The present invention relates generally to an improved data processing system and in particular to a method and apparatus for processing data. Still more particularly, the present invention provides a method and apparatus for processing graphics data.
2. Description of Related Art
Data processing systems, such as personal computers and work stations, are commonly utilized to run computer-aided design (CAD) applications, computer-aided manufacturing (CAM) applications, and computer-aided software engineering (CASE) tools. Engineers, scientists, technicians, and others employ these applications daily. These applications involve complex calculations, such as finite element analysis, to model stress in structures. Often, modeling of these complex structures requires computer generated surfaces and lines that describe the features of physical models. Other applications include chemical or molecular modeling applications. CAD/CAM/CASE applications are normally graphics intensive in terms of the information relayed to the user. Data processing system users may employ other graphics intensive applications, such as desktop publishing applications. Generally, users of these applications require and demand that the data processing systems be able to provide extremely fast graphics information.
The processing of a graphics data stream to provide a graphical display on a video display terminal requires an extremely fast graphics system to provide a display with a rapid response. In these types of graphics systems, primitives are received for processing and display. A primitive is a graphics element that is used as a building block for creating images, such as, for example, a point, a line, a polygon, or text. A primitive is defined by a group of one or more vertices. A vertex defines a point, an end point of an line, or a corner of a polygon where two lines intersect. Data also is associated with a vertex in which the data includes information, such as positional coordinates, colors, normals, and texture coordinates. Commands are sent to the graphics system to define how the primitives and other data should be processed for display.
When lines are displayed on a display screen, a “stair stepping” or “jagged” appearance may be seen depending on the resolution of the display. This visual artifact is a manifestation of a sampling error called aliasing. Graphics adapters typically support a gamma adjustment on a screen or window basis that lightens or darkens the contents of the entire screen or window. Antialiasing techniques are implemented for smoothing or correcting this artifact. These techniques typically specify gradations in intensity of neighboring pixels near the edges of primitives, rather than setting pixels to maximum or zero intensity. These techniques essentially blur the lines by strategically adding pixels with a lower color intensity along the mathematical center of the line. As a result, lines normally one pixel in width are rendered as two or more pixel width lines. These techniques tend to dampen or dilute the intended color intensity for the lines.
Therefore, it would be advantageous to have an improved method and apparatus for correcting artifacts or aliasing in text, points, lines, or triangles.